Many research institutions have been currently conducting research to develop Silicon Carbide (SiC) devices. Advantages of SiC power devices over Si power devices include low on resistance, high switching speed, high temperature operation, etc.
Circuits including bridge circuits have been widely used for switching power supplies and motor driving inverters. In bridge circuits composed of transistors, there is a phenomenon where when a transistor of a one-sided arm is turned ON at high speed, a voltage between gate and source is also changed caused by in the voltage change between the drain and the source of a transistor of the other-sided arm, and thereby causing a malfunction (erroneous turning-on). A short-circuit current due to the erroneous turning-on not only can break the transistors, but also can increase in power loss and cause a noise. In particular, in Metal-Oxide Semiconductor Field Effect Transistors (SiC MOSFETs), since a ratio between a parasitic capacitance Cgs between gate and source and a parasitic capacitance Cgd between gate and drain is small, and the voltage between gate and source is largely changed, and an on-resistance is low, the short-circuit current due to the erroneous turning-on is also increased, and breaking easily occurs.
As a means for suppressing the erroneous turning-on, the inventors have proposed a method of reducing an inductance of a short circuit path between gate and source at the time of transistor-off, by disposing an active mirror clamp circuit between the gate and the source of the SiC MOSFET.
There has also been a method of forming an active mirror clamp region in an inside of a chip.